In performing image analysis over successive fields of view as disclosed in concurrently filed application, entitled Image Analysis Data Transfer, it is often necessary to identify from successive fields of view a specific point related to a feature or object boundary. However, the video signal which defines the feature boundary always contains a small amount of noise and thus points identified in an initial field of scan will not be exactly coincident with points identified using similar criteria on subsequent fields of scan. There will inevitably be a small amount of noise which will displace these points from field to field.
In the copending application, entitled Image Analysis Data Transfer, coordinate data from an initial field of view is stored in a memory to identify points of interest termed index points at which data is to be extracted at subsequent fields of view. These index points can define a position based, at least in part, on information derived from the video signal or a scanner for a television camera as a component of the image analysis system. A description of the function of a television camera in an image analysis system, together with a derivation of data relating to the positions of boundaries, is found in U.S. Pat. No. 3,763,357, entitled "THRESHOLD CIRCUIT FOR CONVERTING A VIDEO SIGNAL TO A BINARY VIDEO SIGNAL," issued Oct. 2, 1973 for inventor Roger R. A. Morton.
In successive fields of scan, electronic measurement logic performs calculations on the video signal and extracts data which was sampled when the scan format was in a position related to the points identified in the initial field of scan. Because of the nature of this extraction in a noise-free system, the synchronism between the coordinates of the stored points and computation of data is inherent in the designed system. However, the addition of noise which will often arise from the video signal due to the action of the television camera preamplifier which injects noise into the initially minute video signal and results in the intercept boundaries, defined in an initial field of scan, falling into a position which differ, possibly significantly, from subsequent fields of scan.